fix(security): stop GET /api/users/:id leaking any user's apiToken and email

[lilyshen0722]

Severity: critical, confirmed by live execution

As a plain, non-admin, verified account I fetched another user's profile on production and received their full Mongo document:

LEAKS apiToken: True  | value present: True
LEAKS email:    xcjsam@g.ucla.edu

apiToken is a working cm_ bearer that authenticates as that user (middleware/auth.ts:41). So any account that could sign up could take over any other account, including admins. 68 verified humans are exposed today.

Cause: toSocialProfile (userController.ts:8) spread userDoc.toObject() wholesale, and .select('-password') was the only thing between the schema and the response.

Fix — two layers

1. Serializer. Credentials (apiToken, agentRuntimeTokens, digestUnsubscribeToken, password) are dropped unconditionally — including from your own profile, since the UI gets a token from POST /api/auth/api-token/generate and never from here. Account-private fields (email, entitlements, token scopes, ban state, preferences, contacts) drop whenever the viewer isn't the owner. Public social fields are untouched.

2. select: false on apiToken. So a credential can't ride along on any incidental query anywhere else, now or in future. Filtering by the field still works (projection ≠ filter), so token auth is unaffected.

The trap in layer 2, and how it's handled

Code that reads the value back now gets undefined unless it asks for +apiToken — and issueUserTokenForInstallation treats an absent token as "none exists" and rotates. That would have silently invalidated the credentials of all 42 agent accounts that hold one.

Every reader is updated explicitly: getOrCreateAgentUser (which backs both the token-issuance and bootstrap paths), the lookup at agentIdentityService:526, and the agent-tokens hasToken probe. I've fingerprinted all 42 tokens pre-merge to verify post-deploy that none rotated.

Test

6 new tests covering the exact exploit (another user can't get the token or email), that your own profile keeps private fields but still never the token, and that the schema field is genuinely select: false.

Two existing mocks returned bare objects where production now chains .select(); both updated to thenable query builders, assertions unchanged. Net test failures vs origin/main: zero (the 3 remaining suite-level failures are the pre-existing Node-26 jsonwebtoken drift, identical on main).

Not in this PR

Also confirmed live and still open: GET /api/pg/pods returns all 229 pods instance-wide including private ones, and POST /api/pg/pods/:id/join let a non-member join a private pod with a 200. Being fixed separately.

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